I'm an educator at the University of South Florida in Tampa, FLorida--a writing teacher, to be specific. Anyway, one of the applications I use a lot is a wiki, specifically, a customized version of Wikki Tiki Tavi. You can see this wiki in action at http://mattbarton.net/tavi
(you'll need to register on my forums to get full access, they're located at http://mattbarton.net/phpBB2
Anyway, wikis are fairly new applications, and not a lot of people have tapped their power. I've tried my best to integrate the concept into PHPBB, but my programming skills are far less adept than yours.
Perhaps you could create a mod for phpbb2 to include wikis? What I imagine is that "WIKI" would be added to the menu bar. When a user clicked it, he or she would see a phpbb2-themed screen, except at the bottom would be a wiki. (There should be an EDIT button there so that anyone could edit the pages..)
What makes wikis useful for writing classes is that (a) they store all versions of a student's work. There is also usually a "compare versions" tool that lets me see how the students worked on their documents as they went along. (b) They enable easy peer collaboration. The students can log in, edit each other's work, etc. This is vital.
The features I'd most like to see in my dream wiki are:
a. Full integration with phpbb2. Maybe this would even change the profile page to show a list of all the wikis created or edited by the users. Also, moving to the wiki wouldn't look like a whole new website! I'd also like to retain phpbb2's editor, though, of course, it'd need some new features (the ability to create wiki pages being the most important.)
b. Intelligent security and permissions. Administrators and moderators, for instance, should be able to 'lock' certain pages from being edited. They should also be able to permanently delete a wiki from the database (the 'deprecate' function in most wikis).
c. Good records, statistics, and monitoring features. Most wikis have an Indexing feature, a "View Recent Changes" option, a Search (it'd be nice if this would search phpbb posts & wikis), and, of course, "View History." I'd like to know who created pages, edited pages, when they did so, and be able to compare the difference.
d. Intelligent Editor. Students typically like to draft in Word and bring it into the wiki. It'd be nice, then, to have a good filter or what-have-you to cull out the Microsoft Word codes. There are some other things I need in the editor-- A 'table' feature and a better way to manipulate images.
Anyway, I'm not sure if you'd be interested in taking on a project like this, but I can offer you something significant in return. Next year (around June) I am presenting a paper on Wikis at CCCC, which is the world's biggest conference for professional writing professors and instructors. I'm on a popular panel, so we expect a huge audience. If you will take this on, I'll certainly plug the hell out of you and your work ! I expect that hundreds of compositionists would want something like this for their classes as well.
I'm more than willing to help you develop the product (error-testing, feedback, etc.) Please let me know what you think.